Cisco Secure Firewall Services Module (FWSM)

Chapter 17 Asymmetric Routing

This chapter provides an overview of asymmetric routing prevalent in the enterprise network. You will learn how the placement of a firewall in a network breaks an asymmetric flow. This chapter also includes designs for symmetric routing with firewalls and covers the FWSM feature that supports asymmetric routing.

In asymmetric routing, the packet traverses from a source to a destination in one path and takes a different path when it returns to the source. Asymmetric routing is not a problem by itself, but will cause issues when Network Address Translation (NAT) or firewalls are used. For example, in firewalls, state information is built when the packets flow from a higher security domain to a lower security domain. ...